L9

Introduction to the Viruses
Virus are extremely small infective agents. obligatory intracellular. A complete particle, or virion , has much simpler structure than a cell. It essentially consist of a block of genetic material (either DNA or RNA but not both) surrounded by proteinaceous coat that protects it from the environmental damage and aid in its transmission from host to host, the protein coat of virus is called the capsid, designed to protect the genome, the capsid and nucleic acid called Nucleocapsid.
The pathogenicity of a virus depends on a great variety of structural and functional characteristics. Therefore, even within a closely related group of viruses, different species may produce significantly distinct clinical pathologies.




DNA Vaccines
DNA vaccines represent a new approach to vaccination. The proposed mechanism for these vaccines can be summarized as follows: The gene for the antigen of interest is cloned into a bacterial plasmid that is engineered to increase the expression of the inserted gene in mammalian cells. After being injected, the plasmid enters a host cell where it remains in the nucleus as an episome (that is, it is not integrated into the cell s DNA). Using the host cell s protein synthesis machinery, the plasmid DNA in the episome directs the synthesis of the protein it encodes. This antigenic microbial protein may leave the cells and interact with T helper and B cells, or it may be cleaved into fragments and presented as MHC I antigen complex on the cell surface, resulting in activation of killer T cells.